With applications entailing the measurement of a bioelectric signal, for example an electrocardiogram signal (ECG signal), via a differential voltage measuring system, it is advantageous to be able to identify whether an electrode of the differential voltage measuring system is connected or not connected to a patient. This in particular relates to applications in which a further action, for example the controlling and/or triggering of an imaging device on the basis of the bioelectric signal, is carried out. If an electrode is identified as being connected even though it is not connected, triggers could be initiated erroneously. If an electrode is identified as not connected even though it is connected, valid triggers could be suppressed. Therefore there is a requirement for electrode status information that indicates whether the electrode is connected or not connected to be determined as quickly and accurately as possible. Hereinafter, an electrode status of an electrode should be understood to mean electrode status information relating to the electrode, wherein the electrode status information indicates whether the electrode is connected or not connected.
The electrode status of an electrode of an ECG system for measuring an ECG signal can, for example, be determined in that the signal quality of the ECG signal is analyzed and, on the basis thereof, conclusions drawn regarding the electrode status. Since an ECG signal can also have multifarious forms when the electrodes of the ECG system are correctly connected to the patient, such an analysis of the signal quality of the ECG signal has to be very tolerant. This means that in many cases it is not possible to identify an open connection quickly, i.e. in fewer than 100 milliseconds, but that a deficient signal quality indicative of an open connection is only identified after an analysis lasting several seconds.
A return-path method for determining the electrode status of a first electrode is, for example, known from [AC12]. In this context, a test current in the nanoampere range is impressed on the first electrode via a current source. If the first electrode is connected, the test current flows through the patient and a corresponding return path connected to the patient via at least one further electrode. The return path can, for example, comprise a measuring path of the differential voltage measuring system and/or a transmission path right-leg drive facility of the differential voltage measuring system. In this case, the voltage effected by the current source at the first electrode is at the most in the millivolt range since the test current in the nanoampere range flows through an impedance, which is at the most in the megohm range. If the first electrode and/or the return path is not connected, the electric circuit is not closed or the impedance to be overcome by the test current is much greater so that the voltage effected by the current source at the first electrode goes to saturation, which can, for example, be identified by a comparator. Due to the required return path, this only enables the electrode status of the first electrode to be determined if at least one further electrode is connected to the patient.
Patent application No 10 2015 202 447.4 describes a differential voltage measuring system with a right-leg drive facility. [VA11] discloses an ECG system with a right-leg drive facility. The person skilled in the art is in particular familiar with is a right-leg drive facility in particular under the term “right-leg drive”, which is abbreviated to “RLD”. In this context, the reference to the right leg is solely based on conventional use. The side of the patient or extremity of the patient to which the right-leg drive circuit, in particular the RLD electrode, is connected is immaterial for the technical effect of the right-leg drive circuit. In the case of a non-conventional connection of the RLD electrode to the patient, it might be necessary to adapt measuring electrodes of the differential voltage measuring system appropriately in each case with respect to the position relative to the RLD electrode.